Radio-frequency edge-gluing process



Feb. 13, 1962 J. w. MANN Erm. 3,021,248

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Feb. 13, 1962 .w. MANN ETAL 3,021,248

RADIO-FREQUENCY EDGE-GLUING PROCESS Filed April 4, 1955 s sheets-sheet ZV7 7633 l Aw E@ U21@ .35mm 66,/ www MM y J INVENTORS X m'l (11 'LU 38dfz/ww MNH/w# L 127 l-27 2,7' 27 ByhM/M v/f@ c CI ci), Arrow/yx Feb. 13,1962 w. MANN ETAL 3,021,248

RADIO-FREQUENCY EDGE-GLUING PRocEss Filed April 4, 1955 3 sheets-sheet swww 3,021,248 RADlO-FREQUENCY EDGE-GLUlNG PROCESS Julius W. Mann andGeorge F. Russell, both of 711 St. Helens Ave., Tacoma, Wash.

Filed Apr. 4, 1955, Ser. No. 499,116 4 Claims. (Cl. 156-274) This caseis al continuation-in-part of our application Ser. No. 208,627, filedlanuary 30, 195l, now abandoned. ln our copending application on acontinuously operated radio-frequency adhesive setter for edge bondingof materials, Serial No. 261,692, filed December 14, 1951, now UnitedStates Patent Number 2,870,808, we set forth apparatus claims while inthe present case We set forth method claims.

In Douglas fir plywood manufacturing, logs of varying quality are peeledfrom blocks or sections or logs on large rotary lathes in lengthscommonly slightly over fortyeight or slightly over ninety-six inches inlength with the grain of the wood. The veneer which results is, for themost part, one-eighth or one-tenth of an inch thick with of course,other thicknesses. The lathes produce continuous strips of veneer whichare clipped to widths varying with the quality of the logs peeled.Defects in the veneer are clipped out. The widths of the veneer rangefrom slightly over four feet in width down to a few inches. The piecesof veneer thus produced are dried and stacked for use in producingeither face or core st ock in the iinal assembly of completed panels. Y

ln the early days of iir plywood, logs of such high quality wereobtainable that it was common to secure clear veneers without defects insuilicient quantity to secure the entire requirements of face stock fromsingle piece veneers without joining small pieces together. Totalplywood output, however, has increased to such an extent that the topquality logs are no longer available in unlimited quantity, so narrowerpieces must be edge-joined for full size veneer. It is common to use lowgrade logs to produce the veneers used for cores or the inside plies ofplywood. The lower grades carry many defects, which when clipped out,leave most of the stock in narrower than four foot widths.

To eliminate core gaps, to make solid face stock, and to produce sounderpanels, it has become the practice of some mills to edge-glue the smallwidth pieces of veneer to secure thereby pieces of full width for easein handling, for reducing cost and to improve quality. Thesesmallerpieces are now edge-glued together mainly by two methods-first, by theuse of a paper tape overlapping two pieces of veneer placed closetogether and, second, by applying a resin adhesive to the edges of theveneer pieces and registering their edges together, under the influenceof steam or hot plates or hot circular drums to cure the adhesive and tosecure a bond between the edges. This produces a continuous strip ofveneer all edge-glued together.

Major drawbacks in the rst or paper tape method arise when the tape issanded off. There is also the weakness of the tape itself and otherhandling dii'liculties arise. ln the second method, the heat of the hotplates or drums employed to cure the resin adhesive, sears and casehardens not only the glue lines but the wood itself, necessitatingstacking the glued veneer for long periods of time to allow the heat todissipate and resulting in major changes in the moisture content of thewood.

ln the manufacture of panels used in furniture and the like products,the faces of core stock are covered with hardwood veneers of many typesand species. These veneers being. sliced from cants of expensive stockare usually thin; on the order of one twenty-eighth of an inch inthickness.

The edges of such veneer are therefore f States Patent present state ofthe art.

tender to rough handling and since the individual pieces are often verynarrow with reference to their length along the grain, it is customaryto edge-glue several pieces to.- gether either in random or matchedgrains to make at single piece of veneer to cover the face of aninexpensive core of lumber. These faces are commonly taped together witha piece of gummed paper overlapping the two edges of the face of theveneer which is exposed after gluing to the core. Sanding off thesetapes sometimes results in the sanding head going completely through theveneers and into the core stock below. The invention herein described isnot intended to be limited to the processing of any one type orthickness of veneer any more than any other grade and the illustrationsherein contained are illustrative only and not limiting as to the extentof edge-gluing either in grade, thickness, width, length or species ofwood being edge-glued.

To overcome the many difculties of edge-gluing by present methods, wehave applied the high-frequency iield of force to the glue line by meansdescribed in this application as novel, new, useful and revolutionary inthe We employ a high-frequency field of force to cure the adhesivebetween the edges of 'the veneer because it polymerizes the adhesive, ifa thermal setting type resin is used; and it softens it if it is athermo-plastic type without imparting to the veneer itself heat in anamount which materially changes the moisture content of the wood as thecure or softening takes place, and because it does nut burn or caseharden the surface of the veneer as in the case of the heated drum typeof splicer and because it abolishes the need of Surface applied tapewhich must later be removed by sanding as in the tape splicer. Thisinvention is commercially adaptable to the production process 0f theplywood, wood veneering and lumber edge gluing industry and has distinctadvantages over present methods of edge bonding. It makes possible acontinuous strip of edge-glued wood in aform immediately usable in acontinuous process of manufacturing plywood which is being now developedand which has been held back because no such process as we here describehas been available to the industry up to this time.

We have invented a process of high-frequency edgegluing as well as meansof and equipment for accomplishing the method, both of which will befully explained hereinafter, but it should be pointed out that manyunique factors must be considered. Plywood veneer when stacked in pilesfor storage absorbs moisture in its exposed edges to a greater degreethan the inside and unexposed portions of the pile. This ripples theedges to such an exten* that a straight-edged surface is sometimesdifficult to find in an inspection trip through a plant. After beingedgespread with a heat responsive adhesive of a type currently availablesuch as ureas, melamines, phenols, resorcins in the thermo-setting typesas Well as the many others in the thermoplastic types, these wavy-edgedveneers must be held in absolute register while being edge-glued, sinceout of register edges would adversely alfect the end result and meansreject panels or faces, uneven cores and non-uniform glue spreads. Aftermany tries at smoothing out the ripples on edges by bending, flexing andother articial means, we determined the ilat plane to be the mostadvantageous in which to carry the veneers while under the influenceofthe glue setting process and that relatively closely spaced V beltsdriven together in a multitude of assemblies would retain the veneer ina relatively tiat plane if corresponding sections of a V belt drive wereused above and below the moving veneer with spacing so close as toprevent the occurrence of any warpage when the veneers come togetheredgwise before gluing and are thereafter retained in register during theglue setting.

Other objects and advantages will appear in the following specification,and the novel features of the device will be particularly pointed out inthe appended claims.

Our invention is illustrated in the accompanying drawings forming a partof this application, in which:

FIGURE l is a schematic side elevation of our radiofrequency edge-gluingpress;

FIGURE 2 is a horizontal schematic section taken along the line II-II ofFIGURE 3;

FIGURE 3 is a transverse schematic section taken along the line III-IIIof FIGURE 2;

FIGURE 4 is an enlarged transverse sectional detail of the skate wheeland electrode support;

FIGURE 5 is a schematic transverse section of a portion of theradio-frequency edge-gluing press and illustrates the electricalcircuits for single strength, stray field, parallel bonding;

FIGURE 6 is a schematic view similar to FIGURE 5, and illustrates theelectrical circuits used in Z pattern parallel bonding;

FIGURE 7 is another schematic view similar to FIG- URE 5 and illustratesthe electrical circuits used in the split pole parallel bonding; and

FIGURE 8 is a schematic longitudinal section through two portions of theedge-gluing press and shows a moditied form of electrode and mountingtherefor.

While we have shown only the preferred forms of our invention, it shouldbe understood that various changes or modifications may be made withinthe scope of the appended claims without departing from the spirit andscope of the invention.

In FIGURES 1 to 3, inclusive, we illustrate one type of press which maybe used for the radio-frequency edgegluing of veneer. FIGURES l and 2show a feed section and a press section and a plurality of belt-driveassemblies A are spaced one from the other the desired distance and aremounted upon shafts 1 and 2 in the feed section. The belt-driveassemblies A include sheaves 3 and 4 mounted on the shafts 1 and 2, andthese sheaves are grooved to receive rubber V belts 5 that haveresilient properties for a purpose hereinafter described. Any means, notshown, may be used for taking up the slack in the belts 5 in order tokeep them taut at all times. The belt-drive assemblies A are designed tobe positioned above sheets of veneer B that are to be fed into themachine for the edge-bonding of the adjacent pieces together. The grainof veneer runs crosswise to the moving direction of the belt-driveassembly A.

The power-driven feed section of the press comprises the belt-driveassemblies A already referred to and these are designed to contact withthe upper surfaces 6 of the veneer sheets B while .a second set ofbelt-drive .assemblies A1 in the feed section of the machine aredesigned to contact with the under surfaces 6a of the same veneer sheetsB. The lower belt-drive assemblies A1 include shafts 1a and 2a whichpreferably parallel the shafts 1 and 2, see FIGURE 1, and are placedbelow the veneer `sheets B. The shafts 1a and 2a carry sheaves 3a and4a, see FIGURE 2 and rubber V-shaped belts 5a are passed around thesheaves. The Vlower reach of each belt S and ,the upper reach of Veachbelt 5a provides a path which will support and move the sheets of veneerthrough the Afeed section of the machine, as clearly shown in FIG- `URE1.

Any means may be used for urging the veneer contacting reaches of thebelts 5 and 5a against the adjacent surfaces 6 and 6a of the veneer B soas to hold `the sheets in a fiat plane. In FIGURES l to 3, inclusive, weshow live upper belt-.drive assembfies A and a like number of lowerbelt-drive assemblies A1 for feeding the sheets of veneer B through thepower-driven feed section of the press. We do not wish to be confined toany exact number -of assemblies nor to the particular type of veneerfeed illustrated because any means for holding the sheets of veneer in afiat plane and moving them from the feed section toward the presssection of the device in an edge to edge abutting relation, may be used.We urge the veneer-contacting portions of the V belts against the sheetsof veneer by the mechanism illustrated in FIGURES 1 to 3, inclusive. InFIGURES l and 4, we show a plurality of wheels 7 such as skate wheels,that are rotatably mounted in a frame 8 and this frame is supported bytransversely extending channel irons 9 that in turn are carried by anI-beam frame 10, FIGURE 4. The wheels 7 are arranged in a row and areplaced as close together as possible and contact with the lower reach ofthe belt 5. The wheels act as a continuous bed of rollers for the lowerreaches of the belts 5.

In FIGURE 4, the skate wheels 7 are mounted between side members Sci-8a,forming the frame 8, and angle irons Sb-Sb secure the frame 8 to thecross channel 9. The lower edges of the side members 8a have guide rods8c welded thereto and these constitute guide beads for the lower reachof the V belt 5. The skate wheels 7 contact with the narrow edge of thelower reach of the V belt 5. The means for mounting the skate wheels 7is illustrative only and we do not wish to be confined to the exactmeans shown.

In FIGURE 1 it will also be noted that we provide a lower set of wheels7a, such as skate wheels, and mount them in a frame 8d, the frame beingsimilar to the frame 8 and urged upwardly by air pressure in hoses 9a.The air hoses 9a extend transversely across the machine and are enclosedin telescoping members 9b that rest on a1 supporting frame 10a and willmove the upper reach of the V-belt 5a against the under surface 6a ofthe veneer B with a yielding pressure. The frame 10a has bearings forrotatably carrying the shafts 1a and 2a and springs 10b yieldinglysupport the frame 10a. The air hose can have any desired pressuretherein and will cause the wheels 7a to exert the desired pressureagainst the V belt portions 5a that contact with the under surface ofthe veneer. The edges of the sheets of veneer B are provided with acoating of adhesive of the desired type before the veneer is fed intothe press.

Any means, not shown, may be used for driving the shafts 1 and 2 and theshafts 1a and 2a for moving the sheets of veneer B from the left handfeed side of FIG- URE 1 toward the right hand press side. The veneer maybe manually fed between the sheaves 3 and 3a or a feeder, not shown, maybe used for this purpose. The upper wheels 7 provide a non-yieldingpressure plate for the veneer. The lower wheels 7a in actual practicewill press the belt 5a against the veneer surface 6a and the portion ofthe belt from the pulley 3a to the lead wheel 7a will extend upwardly ata slight angle to form with the lbelt 5 what we term a "birds mouth. Thefeeding of the veneer is made easier and different veneer thicknessesare compensated for in this manner.

The veneer is fed from the feed section into the pressi section of themachine. This section is preferably a duplicate of the feed sectionexcept that the sheaves and shafts are preferably not power driven andthe purpose of this will be explained hereinafter. The press section maybe power driven if it is thought necessary. Furthermore, it is desirableto have the feed section overlap the press section to a slight extentand therefore 4the forward sheaves of the press section are placedbetween the front and rear sheaves .of the feed sections. For example,in FIGURES l and 2, the press section is shown as being composed of aplurality of upper rubber V-belt assemblies C. The V-belt assemblies `Chave their front shaft 12 mounted between the shafts 1 and 2 andpositioned above the Vsheets of veneer B. The rear shaft 13 of the upperV-belt assemblies C is placed to the rear of the' shaft 2. A sheave 14is mounted on the shaft 12 and a sheave 15 is mounted on the shaft 13for each assemblyl C.` Belts 16 V-shaped in. cross-section are passedaround the sheaves 14 and 1S. It will be noted in FIGURE 2 that the topbelt assembly C of the press section is placed close to one of the topbelt-drive assemblies A of the feed section. We prefer to use as manytop belt assemblies C as there are top belt-drive assemblies A.

It will also be noted in FIGURE l that the bottom V-belt pressassemblies C1 in the press section of the machine have a front shaft 17,and a rear shaft 18. A sheave 19 is mounted on the front shaft 17 whilea sheave 20 is mounted on the rear shaft 18. As many sheaves 19 and 20are placed on the shafts 17 and 18 as are needed to make up the bottomV-belt press assemblies C1. V-shaped belts 21 made of rubber so as tohave resilient properties, are passed around the pairs of sheaves 19 and20. It will be seen from this structure that the rear portions of thebelt feed assemblies A and A1 overlap the front portions of the V-beltpress assemblies C and C1.

There may be slight spacings between the adjacent sheets of veneer asthey are moved through the feed section of the machine, this spacingresulting from the manner in which the pieces of veneer or othermaterial is fed into the machine. This same spacing between adjacentsheets would be maintained in the press section if the V-belt assembliesC and C1 Were driven at the same speed as the V-belt assemblies in thefeed section. If the V-belt assemblies in the press section arepermitted to idle vrather than be driven, the members B moving from thefeed section would abut the members in the press section before theV-belt assemblies C and C1 would be moved. In this way contact betweenthe edges of adjacent members B is established and maintained throughthe press section.

The V-belt assemblies C and Cl have rollers or wheels contacting theportions of the V belts which in turn bear against the upper and lowersurfaces 6 and 6a of the pieces of veneer B. Again referring to FIGUREl, it will be seen that We provide wheels 22 mounted in a frame 23 andbearing against the lower reach of the V belt 16 in the rear upperV-belt assembly C. Channel irons 24, similar to the channel irons 9,support the wheel carrying frames 23. The parts 22 to 24, inclusive,correspond to the parts 7 to 9, inclusive.

Another group of wheels 26 for the lower press assemblies C1 are mountedin a frame 27 and air hoses 28 are placed between the frame 27 and asupporting frame 29 for urging the wheels against the upper reach of theV belt 21. The supporting frame 29 carries the shafts 17 and 18. Weprovide a group of Wheels 26 for the upper reach of each V belt 21, andwe also provide a group of Wheels 22 for the lower reach of each V belt16. The result is a continuous pressure against the portions of the Vbelts that contact with the veneer. Springs 25 yieldingly support theframe 29 in the same manner as the springs b yieldingly support theframe 10a.

The press section comprising the upper and lower V-belt assemblies C andC1 are not only operated by the pieces of veneer B moved therebetween,but in addition an adjustable braking force may be used for retardingthe too free movement of the veneer through the press section ifdesired. The V-belt assemblies A and A1 in the feed section not onlyhold the veneer sheets in a flat plane, but also move the veneer intothe press section. The V-belt assemblies C and Cl in the press sectionnot only maintain the sheets of veneer in the same flat plane, but themovement of the veneer through the press section is preferablyaccomplished by an edge to edge contact between the adjacent pieces ofveneer caused by a forward movement of the sheets in the feed section asthey are fed from this section into the press section. 'Ihis will causethe abutting edges of adjacent sheets of veneer to be held in closecontact as the sheets pass through the press section, and in additionthe abutting edges will be held in perfect alignment as they passthrough the press section. It is possible to power drive the V-beltassemblies in both the feed and press sections and to have the V-beltassemblies in the press section operate at a slower speed. Thisarrangement would not only close the gap between adjacent pieces B inthe press section, but would also apply the desired pressure to urge theabutting edges together so a firm wood to wood contact is maintainedduring the heating of the adhesive.

We apply the radio-frequency heat to the adhesive that is interposedbetween the abutting edges and the heat causes the adhesive to set andthus bond the adjacent sheets of veneer to each other along theirabutting edges to form a moving web of edge-bonded veneers. If it isnecessary to prolong the time of heating, a braking force can be appliedto the V-belt assemblies C and Cl to retard the forward movement of thesheets of veneer B through the press section. In this case the V-beltassemblies in the press section would not be power driven, but wouldidle. Of course the press section V-belt assemblies could be moved at aslower speed than the feed section to accomplish the same result. l

Any braking means may be used and we have shown brake drums 30-31mounted on the shafts 13 and 18 in FIGURE l. Brake shoes 32 and 33 arepivoted at 34 and 35, respectively, and adjustable springs 36 and 37urge `the shoes into frictional contact with the brake drums to createthe desired braking force. This will'cause the edges 11 of the strips ofveneer to remain in contact with each other so that the adhesive 11aapplied to the edges, will be heated by the radio-frequency energy andset so as to bond the adjacent veneer sections into a continuous web.

It is now best to refer to FIGURE 5 wherein we illustrate one method ofparallel bonding for the sheets of veneer that are being moved throughthe press section of the machine. The lower reaches 16a of the V belts16 in the V belt assemblies C are indicated as contacting with the uppersurface 6 of the Veneer B. The same figure also illustrates the upperreaches 21a of the V belts 21 in the V-belt Iassemblies C1 contactingthe under surface 6a of the veneer B. The Veneer will therefore be heldin a fiat plane and its edge 11 will be maintained in a straight line.

We place a plurality of electrodes 3S between the lower reaches 16a ofthe V belts and these electrodes are preferably placed midway betweenthe lower reaches of the adjacent V-belt assemblies C and parallel thelower reaches 16a, see FIGURE 2. The electrodes may be of any lengthdesired and they preferably extend throughout the length of the presssection as shown in FIG- URE 2.

Again referring to FIGURE 5, it will be seen that every other electrode38a, 38c and 38e starting from the left hand side of the figure iselectrically connected to one side 39 of a radio-frequency coil 40. Inlike manner the remaining electrodes 38b, 38a' and 381 are electricallyconnected to the other side 41 of the radio-frequency coil 40. Theradio-frequency coil preferably forms a part of the radio circuit shownin our Patent No. 2,506,158, issued May 2, 1950. Since theradio-frequency current owing through the coil 40 alternates, theelectrodes 38a, 38C and 33e will be positive at one instant while at thesame time the electrodes 38h, 38d and 38j will be negative. When thecurrent reverses itself in the coil, the positive electrodes will becomenegative and the negative ones will be changed to positive.

The use of elongated electrodes 33 are employed to answer therequirement that the glue plane 11a shown in FIGURE l, be under theinfluence of the high-frequency field for a considerable duration oftime compared to that of an instantaneous exposure, should theelectrodes be short in length. A special characteristic of thehigh-frequency field of force should be understood to be able to fullyappreciate the reason for the particular arrangement herein disclosed.When alternately charged spaced electrodes connected to a source ofhigh-frequency alternating current are arranged so as to have parallelfaces, they alternately possess opposite electrical charges which are instep with the frequency of the generated source of radio-frequencyenergy. The field between adjacent electrodes 38 will be relativelynon-uniform, varying from one electrode of a high negative charge suchas the electrode 38b in FIGURE 5, to a Zero electrical charge midwaybetween the electrode 38b and then to either the electrode 38a or theelectrode 38e which have a positive charge. The peculiar characteristicof the high-frequency standing w-ave field, set forth in our patentabove-mentioned, has led us to the invention of the novel electrodearrangement herein described and the method of edgebonding hereindisclosed.

The point X midway between parallel electrodes oppositely charged is apoint of zero electrical charge and hence a V belt such as the one shownat 16a in FIGURE 5, or even a metal shaft, chain, plate or the like, canbe placed midway between the electrodes 38a and 38h withoutsubstantially affecting the distribution of the electric field of forcebetween the oppositely charged and parallelly faced electrodes. So longas the distribution of capacity along the length of the electrodes andbetween the electrodes and the mass placed midway therebetween does notvary substantially throughout the electrode length, the zero electricalcharge will be in the vicinity of the V-belt portion 16a. The exactplacing of the belt at the midway position is not critical, but varieswith the width of the mass employed between the charged electrodes inrelation to the total width between the parallel electrodes.

The electrodes 38 are preferably spaced apart the same distance as arethe V-belt portions 16a. The electrical connections between theelectrodes 38 and the coil 48 are designed so as to feed into the upperframework of the V-belt assemblies C as shown in FIGURE 5. `It isobvious that the electrical network could be placed in the lower V-beltassemblies C1.

It is advisable that the electrodes 38 actually contact with the wood Bas it moves through the machine. If there are air spaces or if there isa non-uniform contact between the electrodes and the wood, electricsparks or undesirable arcs may be induced. It is also -necessary thatthe edges of the pieces of veneer contact each other throughout theirlengths so that no voids will be formed, across which undesirable arcingmay take place when establishing contact between the electrodes and thesheets of veneer B. The electrodes 38 are preferably suspended fromrods. FIGURE shows a simple arrangement with the electrodes 38 beingsupported by rods 42. The rods in turn are suspended from bus bars 43and electrical insulators 44 connect the bars to the machine. The busbars l43 preferably extend transversely across the machine. One set ofbus bars will be connected to the electrodes 38a, 381: and 38e, whileanother set will be connected to the other electrodes 38b, 38d and 381We do not wish to be confined to this particular type of support for theelectrodes 38 because any means for supporting the electrodes andholding them in contact with the veneer would suice.

The principle taught by us in our Patent No. 2,434,573, is that parallelbonding utilizes that path for the eld of force which is more conductivethan some other path, and places such a more conductive path parallel tothe dominant field lines of force of an electric field when the eld isestablished between alternately and oppositely charged electrodes suchas for example, the electrodes 38a and 38b. The glue plane 11a shouldsubstantially parallel a straight line connecting the alternatelycharged electrodes 38a and 38b at their closest points. All of theelectrodes 38a through 38j, inclusive, in FIGURE 5, are parallel bars ortubes and it will be seen that an infinite number of lines may be drawnbetween the adjacent electrodes 38a and 38h for example, and these lineswill be parallel to each other. The passage of a glue plane 11a throughthe machine will cause this plane to parallel the radio-frequency linesof force just mentioned.' The glue plane 11a will be substantiallyperpendicular to the running direction of the V-belt portions 16a. Theradiofrequency will therefore pass along the glue planes from oneelectrode to the other and this will cause the adhesive to set. Thediagrammatic view of FIGURE 5 is of a single strength stray fieldparallel bonding.

When gluing thicker pieces of lumber together, the Z pattern parallelbonding arrangement shown in FIGURE 6 may be used. The same upper andlower V-belt assemblies C and C1 are employed so that the lower reach16a of each upper V-belt assembly C and the upper reach 21a of eachlower V-be't assembly C1 will hold the thicker pieces of lumber B1 inthe desired position. Boards of random width may be glued togetheradjacent to their ledges 47.

In our Patent No. 2,457,498 on Z pattern parallel bonding, we disclosecorrugated electrodes which provide staggered points that contacted theedge-glued boards on opposite surfaces. rI`his arrangement concentratedthe field lines of force in the glue plane to form a zig-zag or sawtoothpattern rather than spot gluing or solid gluing. The Z pattern type ofparallel bonding can be used with the :machine shown in FIGURES l to 3,inclusive, but the network of electrodes 48 and 49 would have to bealtered from the electrodes 38 shown in FIGURE 5.

In FIGURE 6, we show the electrodes 48a and 4Sb placed above the pieceof lumber B1. Between the electrodes 48a and 4817, two of the V-beltassemblies C are disposed. There will therefore be two of the lowerreaches 16a of the V-belts placed between the pair of electrodes. Theother set of electrodes 49a and 4911 are disposed under the piece oflumber and here again two of the upper reaches 21a of the lower V-beltassemblies C1 will be disposed between the pair of electrodes. Theelectrodes 49a and 49h are connected by wires to an end 50 of aradio-frequency coil 51, and wires lead from the electrodes 48a and 48bto an end 52 of the radio-frequency coil 51. The coil forms a part ofthe radio-frequency circuit shown in our Patent No. 2,506,158.

At any given instant the electrodes 49a and 49b are positive while theelectrodes 48a and 48b are negative and when the alternating currentreverses itself, the reverse is true. Radio-frequency lines of forcewill therefore be established from the negative electrode 48a to thepositive electrode 49a and then from the same positive electrode 49a tothe negative electrode 48b, and finally from the negative electrode 48bto the positive electrode 49b, as shown by the dash Z pattern line inFIGURE 6. If more electrodes are used the zig-zag, the s'awtooth or Zpattern would merely be increased in length. The Z pattern should extendthroughout the entire length of the glue plane 47a provided on the edge47 of the piece of lumber B1.

It will be found less necessary as the thickness of the stock increases,to have the V-belt assemblies placed close together. When one-inchboards are glued together, the V-be';t assemblies may be spaced fourinches apart instead of two or three inches apart as is the case whenstock 1A() of an inch thick has its edges bonded together. As thethickness of the stock increases, the necessity to maintain closecontrol of the stock edge registration diminishes.

Furthermore, as the thickness increases, it will be found that at acertain point Where a full and symmetrical cure in the adhesive line orplane is desired, two sets of electrodes of the type shown in FIGURE 7can be used. We term this arrangement of electrodes, split pole parallelbonding. Again, the lower reaches 16a, of the upper V- belt assemblies Ccontact with the upper surface of the piece of lumber B2 at the sametime the upper reaches 21a of the lower V-belt assemblies C1 contactwith the under surface of the same piece of lumber. An electrode 53 isplaced between each pair of lower reaches 16a. In like manner anotherset of electrodes 54 contacts with the "spare-is under surface of thepiece of lumber B2 and an electrode is placed between each pair of upperreaches 21a of the V-belt assemblies C1. Every other electrode in theupper group, namely: the electrodes 53a and 53e are connected to an end55 of a radio-frequency coil. It will further be Seen that theelectrodes 54a Land 54e in the lower set which are disposed directlyunder the upper electrodes 53a and 53e, are also connected to the sameend of the coil. For example, the electrodes 54a and 54C will beconnected to the same end 55 of the coil 56. The other pairs ofelectrodes 5311 and 54h, and 53d and 54d will be connected to theopposite end 57 of the radio-frequency coil 56.

The result is a split pole eectrode network. At any given instant, theelectrodes 53a, 53C, 54a and 54C, will be charged positive, while at thesame time, the other electrodes 53b, 53d, 5412 and 54d, will benegatively charged. When the electrodes are placed midway between the V-belt assemblies, as indicated in FIGURE 7, and as the spacing betweenthe belts is increased, the pairs of electrodes each forming a splitpole, will be spaced further apart from each other. If, at the sametime, the thickness of the board is increased, requiring a deeperpenetration of radio-frequency lines of force to cure a wider glue planedepth, then there comes a point as the thickness of the board increases,where a parallel network of electrodes below the board can duplicate thework performed by the electrodes placed above the board. Such a case isdepicted in FIGURE 7 and the electrical charges on the electrodes in theupper group will be the same as the electrical charge on the lowergroup. This we term split pole parallel bonding and we refer to thismethod of bonding in our co-pending application Serial No. 208,626, nowPatent No. 2,678,897, issued May 18, 1954.

It will be seen, therefore, that several choices of wiring arrangementare available to the user even though the same type of press as shown inFIGURES l to 3, inclusive, is employed. The choice of bonding methoddepends upon the thickness of the lumber which is being edge-glued. Eacharrangement shown in FIGURES 5, 6 and 7, has a distinct advantage for aparticular spacing of the V-belt assemblies and for the particularthickness of the wood being edge-glued. The electrode network in FIGURES5, 6 and 7 is long enough to give exposure time for curing ureaadhesives in relation to the characteristics of the resin and the speedof movement. In gluing veneers edge to edge, a speed of twenty to thirtyfeet per minute is sutlicient. The speed is slower when edge-gluingpieces are used to make up chair bottoms.

The radio-frequencies used range from six to just over forty megacycles.Other frequencies may be employed, however, and we do not wish to beconfined to the frequencies mentioned.

Little has been said as to the possibility of the stock buckling oroverlapping in its transfer from the feed to the press section or onactual edge to edge contact between fast moving veneers and thosealready edge contacting whether the contact be made in the press sectionor in the feed section or in an overlapping portion of the two sections.It was found that if the feed and press sections overlapped slightly, abetter transition and contact can be expected. If the upper V belts A ofthe feed section therefore enclose besides their own two shafts, theleading common shaft of the upper unit of the press section C and the Vbelts spaced between the sheaves of the other section, an overlapping ofthe feed and press sections may be employed with good results. Withoutthis overlapping, edge register could not be maintained between thepieces being bonded without complicated mechanical structures beingrequired. When the multiplicities of V-belt assemblies are spaced twoand one-half inches apart in the feed and press sections, they will bespaced only one and one-quarter inches apart in the overlapping portionof the two sections. This forms a firm table where edge contact may bemade without the feat of buckling or the over-creeping of veneers oneupon the other-even if of this cross section and Width. This overlap ofthe two sections should be long enough so that as the veneer leaving thefeed section passes the last skate wheel roller 7 holding its V beltflat from the inside, will immediately enter the press section and thefirst skate wheel roller 22 of the press section holding its V belt inposition from the inside. The overlap acts as though no gap existsbetween the feed and the press section. A rm backing of the veneer isaccomplished in the initial portion of the press section due to thisoverlapping feature.

Varying degrees of edge pressure may be applied to the veneers beingpressed together by either one of the two means: (l) by increasing ordecreasing the pressure applied to the opposing sets of skate wheels 22and 26; or (2) by increasing or decreasing the drag which may be appliedto the press section. In the rst case, the compressed air to the hosesections 28 is increased to the desired extent. In the second case, thebrake shoes 32 and 33 apply the desired braking force on the brake drums20 and 31.

The veneer pieces B are run through the machine so the grain of the woodis perpendicular to the running direction of the V-belt assemblies ofthe press section. The glue planes between the abutting edges ofadjacent pieces of veneer will likewise be in the direction of the grainof the wood. Tapered pieces of veneer may be inserted in the webintentionally to correct malalignment of the veneer web as it progressesthrough the machine.

Heat responsive adhesives of the thermal setting type cure in a welldefined time-temperature relationship. Therefore an instantaneousexposure at one point to a hilgh-frequency alternating current field offorce would in most instances be insufficient exposure to polymerize theresin adhesive. Longer exposure allows the internal heat introduced intothe adhesive line by the high-frequency eld to bring the temperature ofthe glue plane up to that required to turn over or polymerize the resin,and to fulfill the basic requirements of the adhesive to cure in acertain time and at a certain temperature.

The V-belt assemblies A1 in the feed section can be moved as a unit andindependently of the V-belt assemblies C1 in the press section. Theamount of compressed air in the air hose sections 9a controls thepressure exerted by the frames 8d with their wheels '7a against theundersurface 6a of the veneer B. In like manner, the amount ofcompressed air in the air hose sections 28 controls the pressure exertedby the frame 27 and wheels 26 against the undersurface of the veneer. Itis possible for example to place two pounds of air pressure in the lefthand hose 9a in FIGURE l, ten pounds in the right hand hose 9a, and thenplace two pounds in the left hand hose ZS and ten pounds in the righthand hose 28.

The air hose will also permit pieces, wedge-shaped in cross section tobe edge-glued. For example, shingles can be fed through the machine andedge-glued together. The thicker butt ends of the shingles would beplaced near one side of the machine and the thin ends would bepositioned near the other side; The hose sections 9a and 28 wouldaccommodate the V-belt sections A1 and C1 to the shingles even thoughthey were wedge-shaped in cross section.

In certain cases where thicker lumber is being edgeglued, the presssection V-belt assemblies C and C1 do not offer suicient retarding forceto the pieces to hold them in contact with each other with sufficientpressure to provide a good bond during the curing of the adhesive. Thisis true even if a braking force is exerted by the brake shoes 32 and 33on the drums 3i) and 31. We therefore show in FIGURE 1, an auxiliary airpressure controlled means for retarding the movement of the boardsthrough the machine to the desired extent.

A stationary member 58 contacts with the upper surface 6 of the web ofveneer B just as it leaves the press sectionof the machine. A movablemember 59 yieldingly contacts with the undersurface 6a of the veneer webB and an air hose 60 applies the desired amount of pressure on themember 59. The air hose 60 has compressed air therein at a pressure ofabout sixty pounds per square inch when thicker lumber than the veneer Bis being edgeglued. A great deal of force is needed to move the thickerlumber between the members 58 and 59 when a clamping pressure of aboutsixty pounds is being exerted. The pieces in the press section will movemore slowly and will be held more tightly together resulting in a moreperfect bond.

In FIGURE 8, We show electrodes of a different shape from those shown inFIGURES 1 to 5, inclusive. Instead of rods 42 connecting the electrodes38 to the bus bars 43 as illustrated in FIGURE 5, the electrodes 61 and62 have upwardly bent ends. In actual practice, the base portions 61aand 62a of the electrodes 61 and 62 would lie in the same horizontalplane and bear against the upper surface 6 of the veneer B. The movementof the veneer through the machine is in the direction of the arrows 61.When the electrode 61 is charged positive, the electrode 62 will becharged negative, and vice versa. The two electrodes 61 and 62 would bespaced from each other in much the same manner as the electrodes 38 inFIGURE 5 are spaced apart.

The bus bars 63 are similar to the bus bars 43 of FIG- URE 5 and supportthe upturned ends 61h and 61C of the electrode 61. Insulators 65 supportthe bus bars 63 and the bars are in electrical connection with one endof a radio-frequency coil, not shown, of the type illustrated in FIGURE5. In like manner, the bus bars 64 support the upturned ends 6217 and62C of the electrode 62.y Insulators 66 support the bars 64 and the barsare in electrical connection with the other end of the sameradiofrequency coil. The bars 64 lie in the same plane as the bars 63.If desired, the insulators 65 and 66 may be spring suspended, by usingcoil springs 67.

Although the ends 61b and 61C of the electrode 61 extend upwardly andrearwardly at an angle and the ends 62b and 62C of the electrode 62extend upwardly and forwardly at an angle, the base portions 61a and 62aof the two electrodes are of the same length and contact with the veneeror other piece being edge-glued, at approximately the same transversepoint. The arrangement makes it possible for the bus bars 6-3 and 64 tolie in the same plane and the base portions of the electrodes to occupythe same relative positions when considering the length of the machine.Of course the base portions 61a and 62a of the electrodes 61 and 62 arespaced from each other. The bus bars 63 and 64 will also be spaced fromeach other.

FIGURES 2 and 3 illustrate the V belts C and C1 in the press section asbeing placed adjacent to certain V belts A and A1 in the feed section.In actual practice we have found it advisable to position the V-beltassemblies C and C1 in the press section, midway between the adjacentV-belt assemblies A and A1 in the feed section. A more uniform pressureon the sheets of Veneer B or other material results from thisconstruction as the material passes from the feed section into the presssection, and therefore we do not wish to be confined to the particulararrangement of the V belts illustrated in FIG- URES 2 and 3. The equalspacing of the V-belt assemblies C and C1 between the V-belt assembliesA and A1 not only causes a more uniform pressure on the material beingglued at the point of transition from the feed to the press section, butalso produces increased pressure on the material at this critical pointof travel through the machine.

The electrodes 38 are also preferably positioned midway between theadjacent V-belt assemblies C and C1. This arrangement is clearly shownin FIGURES 2 to 7, inclusive. Where the overlapping portions of theV-belt assemblies C and C1 in the press section are disposed midwaybetween the adjacent V-belt assemblies A and A1 in the feed section, theforward ends of the electrodes 38 will terminate at points adjacent tothe sheaves 4 and 4a, because the electrodes will be in line with theV-belt assemblies A and A1 in the feed section.

In FIGURE 3 the left hand electrode 38 is shown disposed closer to theV-belt assembly A in the feed section than the next electrode 38, butreference to FIGURE 2 illustrates the V-belt assembly C in the presssection is disposed adjacent to the left hand V-belt assembly A inFIGURE 3 and therefore in reality both electrodes 38, disposed onopposite sides of the uppermost V-belt assembly C shown in FIGURE 2,will be spaced equal distances from their common V-belt assembly C. Theleft hand V-belt assembly C in FIGURE 3, corresponding to the uppermostV belt C in FIGURE 2, is not shown in FIGURE 3 because the drawing wouldbecome too cornplicated. The point that We wish to advance is that theelectrodes 38 will be spaced midway between adjacent V-belt assemblies Cor C1 in the press section.

The underlying principle in using resilient rubber belts in the feed andpress sections and in power driving the belts 5 and 5a in the feedsection while retarding the movement of the belts 16 and 21 in the presssection, is to maintain continuously the edge pressure between adjacentpieces of veneer or lumber, by using the resilient properties of therubber belts 5, 5a, 16 and 21. The lower reaches of the belts 5 incontacting with the upper surfaces of the veneer strips B are in astretched state due to the fact that these reaches are pulling theVeneer strips through the feed section. The same is true of the upperreaches of the belts 5a when contacting with the under surfaces of theveneer strips B and this is due to the fact that these reaches arepulling the veneer through the feed section.

When the veneer strips B reach the press section and are engaged ontheir upper and lower surfaces by the lower reaches ofthe belts 16, andthe upper reaches of the belts 21, these reaches are moved only by theveneer strips entering therebetween. The veneer strips as they move fromthe feed section into the press section, have their adjacent edgesbrought into abutting relation because the veneer strips in the exit endof the press section must move the strips into the press section by edgeto edge contacting therewith. The reaches of the belts in the presssection that are engaged by the veneer strips are therefore placed undercompression. The stretched state of the belt reaches in the feedsection, oppose the compressed state of the belt reaches in the presssection and, as a result, a continuous edge pressure between adjacentpieces of veneer is maintained while the stock is advancing through thehigh-frequency electric field.

The process is also unique because the intermeshed top tractors A and C,and the intermeshed bottom tractors A1 and C1, never release their edgeregister holding of the veneer strips during the transition of the stillunset joints as the strips move from the drive or feed section into theidling or press section. In summing up it will be seen that:

(l) The use of rubber belts to utilize their resilient properties tomaintain edge pressure between adjacent pieces of veneer or lumber isunique.

(2) The intermeshed tractors A and C and A1 and C1 insures the completeregistry of the opposed edges of the adjacent pieces of veneer or lumberduring transit of the stock through the intermeshed portions and onthrough the remainder of the press section.

(3) The combination of the stray field parallel bonding as illustratedin FIGURE 5, and the split pole type parallel bonding, shown in FIGURE7, with the intermeshed tractors is also unique. The contact of the beltreaches with the stock is made at the neutral points of thehigh-frequency eld through which the stock travels in the press section.

We claim:

1. In a continuous method of bonding dielectric materials lying in asingle layer and in abutting relation with adhesive therebetween; whichcomprises the steps: establishing a high-frequency field of force withat least one Zero voltage gradient extending along a path in the field;continuously moving the pieces of dielectric material through the eldwhile maintaining adjacent pieces in contact with each other and in asingle flat plane; and in applying pressure from opposite surfaces ofthe pieces for holding the pieces in a at plane while still permittingthem to move continuously, the pressure on the surfaces being at pointsalong the path of the zero voltage gradient.

2. In the herein described continuous method of edgebonding plurality ofat members together into a unitary at web structure, the steps of:applying adhesive to at least one edge of each flat member, which edgeis to be bonded to a confronting edge of an adjacent fiat member;contacting the flat members from opposite sides at points directly aboveand below each other, the pairs of points of contact being spacedlaterally across the widths of the at members and being used forgripping and continuously moving the at members in yielding processionalrelation following one behind the other with the flat members being heldin the same flat plane; yieldingly contacting the moving leading atmember and progressively contacting succeeding flat members fromopposite sides and at spaced points that lie between the original pointsof Contact for maintaining the leading flat member and the succeeding atmembers in a at plane and thereafter freeing the original points ofContact on the leading at member and successively on the succeeding atmembers; whereby the next succeeding continuously moving at memberfollowing the leading at member will be brought into abutting yieldingcontact with the leading at member and will abut thereagainst at acertain pressure for continuing to move the leading at member, and thesucceeding ilat members will be brought progressively into abuttingcontact with the at member thereahead to form a continuously moving unitcomposed of the at members; and in directing radio-frequency lines offorce through the adhesive planes while the abutting fiat members areyieldingly held in contact while maintained in continuous movement forsetting the adhesive and edge-bonding the flat members together.

3. In a continuous flat plan process of edge bonding flat memberstogether which comprises the steps: gripping a plurality of adhesiveedge spread flat members at transversely spaced apart points above andbelow the members for holding the members in a ilat plane and moving themembers forwardly in a continuous manner; gripping the same flat membersat transversely spaced points above and below the members and betweenthe points already gripped and prior to the releasing of the rst grippedpoints, and applying a less retarding force on the second gripped pointsthan on the forward driving force to apply edge pressure betweenadjacent members while permitting continuous movement of the members toform a web.

4. The sequence of steps as set forth in claim 3: and exposing the webof continuously advancing members in edge abutting pressure appliedrelationship to the heating effect of a high frequency alternatingcurrent field of force during the second gripping of the members andafter releasing the irst gripping of the members for edge bonding theplurality of flat members into a unitary at structure.

References Cited in the tile of this patent UNITED STATES PATENTS1,199,818 Peck Oct. 13, 1916 1,702,185 Weber Feb. 12, 1929 2,303,087Neller NOV. 24, 1942 2,434,573 Mann et al. Jan. 13, 1948 2,453,185Bilhuber Nov. 9, 1948 2,544,133 Carlson Mar 6, 1951 2,571,604 PayzantOct. 16, 1951 2,599,930 Mann June 10, 1952 2,617,752 Hauteville Nov. 11,1952 2,620,837 Quick Dec. 9, 1952 2,633,166 Gillespie et al Mar. 21,1953 2,678,897 Mann et al May 18, 1954 2,708,649 Cunningham May 17, 1955

1. IN A CONTINUOUS METHOD OF BONDING DIELECTRIC MATERIALS LYING IN ASINGLE LAYER AND IN ABUTTING RELATION WITH ADHESIVE THEREBETWEEN; WHICHCOMPRISES THE STEPS: ESTABLISHING A HIGH-FREQUENCY FIELD OF FORCE WITHAT LEAST ONE ZERO VOLTAGE GRADIENT EXTENDING ALONG A PATH IN THE FIELD;CONTINUOUSLY MOVING THE PIECES OF DIELECTRIC MATERIAL THROUGH THE FIELDWHILE MAINING ADJACENT PIECES IN CONTACT WITH EACH OTHER AND IN A SINGLEFLAT PLANE; AND IN APPLYING PRESSURE FROM OPPOSITE SURFACES OF THEPIECES FOR HOLDING THE PIECES IN A FLAT PLANE WHILE STILL PERMITTINGTHEM TO MOVE CONTINUOUSLY, THE PRESSURE ON THE SURFACES BEING AT POINTSALONG THE PATH OF THE ZERO VOLTAGE GRADIENT.